This genetic disorder (autosomal dominant inheritance with high penetrance) disrupts calcium sensing, resulting in inappropriate parathyroid hormone (PTH) release despite normal or mildly elevated serum calcium levels. The inactivating mutation affects the calcium-sensing receptors in the kidney, resulting in enhanced tubular calcium and magnesium reabsorption. Affected individuals present with typically asymptomatic hypercalcemia with normal or mildly elevated PTH levels as well as hypermagnesemia. This disorder can be distinguished from frank hyperparathyroidism by measuring urinary calcium excretion. In familial hypocalciuric hypercalcemia, urine calcium excretion is reduced, and in hyperparathyroidism, urine calcium excretion is increased.

Classic presentation includes:

• Hypercalcemia
• Hypocalciuria
• Hypermagnesemia